The present invention relates to a stern tube sealing apparatus for a vessel.
Conventionally, a stern tube sealing apparatus with a seal ring made of an elastic material has been used for a vessel. However, since a draft pressure is increased in accordance with the vessel getting larger in size, a pressure applied to the seal ring is increased and many troubles that the seal ring is damaged are caused, so that a seawater enters into the vessel and a disadvantage is generated on maintaining the vessel. Accordingly, conventionally as a countermeasure therefor, it has been intended that the entering of the seawater is sealed and a durability of the seal ring is improved by supplying a pressurized air having a pressure slightly higher than the draft pressure to an aftermost annular space formed by a first seal ring and a second seal ring and always discharging the air from the annular space to the sea side.
In this case, when the air is fed out to the sea as mentioned above, a load of the first seal ring is reduced, however, the first seal ring becomes dry by the air, so that a sliding contact surface may be abraded. When the abrasion is generated in the first seal ring, a little amount of seawater enters, water is evaporated within a rearmost chamber and salt is crystallized, so that the salt is attached to the seal ring and a liner so as to be solidified, whereby there are generated disadvantages that the abrasion of both elements is promoted or that a drain line is clogged. Further, a foreign substance such as a marine growth, mud or the like attached to the first seal ring on the seawater side enters into the rearmost chamber, thereby further abrading the seal ring and the liner.
The present invention is made on the basis of the matters mentioned above, and an object of the present invention is to provide a stern tube sealing apparatus which prevents an abrasion by cooling and lubricating a sliding contact surface of a first seal ring, prevents a foreign substance and a seawater from entering so as to further improve a durability of a seal ring and a liner, intends to make the sealing apparatus compact and reduce a cost by using no pressurizing apparatus, and has a high reliability of a seal system.
In order to achieve the object mentioned above, in accordance with a first aspect of the present invention, there is provided a stern tube sealing apparatus comprising a plurality of seal rings slidably brought into contact with a liner of a propeller shaft, wherein piping communicating with one of a liquid reservoir tank and a pressure control valve connected to a liquid supply source is provided in a stern annular space defined by a first seal ring arranged on a stern side and a second seal ring adjacent to the first seal ring, and feeding means for forcibly feeding the liquid in the stern annular space to an outside of a vessel having a higher pressure than that in the stern annular space at a time of shaft rotation is provided on at least one of a sliding contact surface of the first seal ring and an opposing sliding contact surface with which the first seal ring is slidably contact.
The feeding means in this case includes all of means for feeding out a liquid from a low pressure side of the seal ring to a high pressure seawater side thereof to be sealed due to a pumping effect by a seal ring at a time of the shaft rotation (including a time of regular rotation and a time of reverse rotation of the propeller). Further, the seal ring corresponds to an idea including a lip type seal ring, a face type seal ring and a mechanical seal. In the case of the lip type seal ring, the seal ring provided with the feeding means is not required to always have a feature that the lip is directed to the seawater side, for example, it is sufficient that a contact angle with respect to the liner on the seawater side is greater than that on the vessel interior side.
When the structure is made in the manner mentioned above, it is possible to keep a pressure within the stern annular space lower than a pressure on the seawater side, it is possible to feed the liquid to the seawater side and it is possible to simultaneously cool and lubricate the sliding surface of the first seal ring, whereby it is Possible to prevent the foreign substance and the seawater from entering and the sliding load of the second seal ring with respect to the liner is reduced under a low pressure.
In this case, the feeding means for feeding the liquid from the low pressure side of the seal ring to the high pressure seawater side to be sealed is not required to be always provided on the seal ring, and when the feeding means is provided on the opposing sliding contact surface with which the first seal ring is slidably contact, the same functions and effects as those in the case that the feeding means is provided on the first seal ring can be obtained. Further, the feeding means may be provided on each of the sliding contact surfaces of the first seal ring and the opposing element. In the case of the lip type seal ring, the opposing element with which the seal ring is slidably brought into contact is a liner.
Further, in accordance with the present invention, there is provided a stern tube sealing apparatus as recited in the first aspect mentioned above, wherein a branch pipe with a pressure control valve and a flow control valve connecting to the liquid supply source is provided, via a first change-over valve, in the middle of the piping communicating with the liquid reservoir tank and the aftermost annular space, and a constant flow amount valve making it possible to flow out a constant flow amount of liquid from the stern annular space to the outside of the vessel in accordance with a change-over operation of the first change-over valve is interposed in the branch pipe.
In the case that the structure is made in the manner mentioned above, the constant flow amount valve is operated due to changing over the flow passage by means of the first change-over valve so as to flow the constant flow amount of liquid from the first seal ring to the outside of the vessel even when the feeding means does not effectively function, whereby the cooling and lubricating state of the sliding contact surface in the first seal ring can be maintained, and further it is possible to prevent the foreign substance and the seawater from entering.
Further, the first seal ring is generally arranged at the rearmost position (a position closest to the seawater), however, at least one auxiliary seal ring may be further arranged on the seawater side and the feeding means is provided in at least one of the auxiliary seal ring and an opposing element on a sliding contact surface between the auxiliary seal ring and the opposing element. In the case that the auxiliary seal ring is the lip type seal ring, the opposing element is a liner. When the structure is made in this manner, it is possible to further improve a reliability of the feeding effect.
In this case, as mentioned above, the feeding means for feeding out the liquid with a pumping action, or pump-in-action from the low pressure side of the seal ring to the seawater side corresponding to the high pressure side to be sealed is not particularly limited, however, the structure may be made such that a fine unevenness or a fine screw groove is formed on the seal ring and/or the opposing element in the seal ring and the opposing sliding contact surface. A shape of the unevenness is not limited to a circular shape, an angular shape or the like. Here, with respect to a magnitude of the xe2x80x9cfinexe2x80x9d evenness, the unevenness can be realized in a range of height between some microns and some hundreds microns, however, in order to achieve an effective feeding function, some tens microns is desirable. Further, a magnitude of the xe2x80x9cfinexe2x80x9d screw groove is set to be wide since a desirable value changes in accordance with an angle and a depth of the screw or the like, however, a width and a depth of the screw groove are set to a range between some microns and some hundreds microns. In the case of employing the former means, the fine unevenness applies a fine wedge effect to a lubricating film of the liquid at a time of the shaft rotation so as to feed out the liquid from the sliding contact surface to the seawater side. Further, in the case of employing the latter means, the fine screw groove applies a hydrodynamic effect as screw type viscoseal at a time of regular rotation of the propeller so as to feed out the liquid from the sliding contact surface to the seawater side.
Further, in accordance with a second aspect of the present invention, there is provided a stern tube sealing apparatus comprising a plurality of seal rings slidably brought into contact with a propeller shaft liner, wherein piping communicating with one of a liquid reservoir tank and a pressure control valve connected to a liquid supply source is provided in a stern annular space defined by a first seal ring arranged on a stern side and a second seal ring adjacent to the first seal ring, a rubber or polymer resin sleeve for separating into a front chamber directly connected to the piping and a rear chamber is arranged within the stern annular space, and a fine screw groove for forcibly feeding the liquid in the front chamber to the rear chamber at a time of regular rotation of a propeller is provided on a sliding contact surface of the sleeve and/or a sliding contact surface of the liner where the sleeve and the liner are slidably contact with each other.
In this case, the front chamber separated by the sleeve in the stern annular space corresponds to a section area positioned on an interior side of the vessel, and the rear chamber corresponds to a section area positioned on the seawater side.
When the structure is made in the manner mentioned above, the fine screw groove formed on the sliding contact surface of the sleeve within the stern annular space feeds out the liquid from the front chamber to the rear chamber in accordance with a hydrodynamic effect as screw type viscoseal at a time of regular rotation of the propeller, and the liquid leaks out from the rear chamber to the seawater side with passing through the sliding contact surface of the first seal ring.
The fine screw groove mentioned above is not limited to be formed on the sliding contact surface of the sleeve, and the same functions and effects as those in the case of being formed on the sleeve can be obtained even when being formed on the sliding contact surface of the liner with which the sleeve is slidably brought into contact.
Further, in accordance with the present invention, there is provided a stern tube sealing apparatus as recited in the second aspect mentioned above, wherein the structure may be made such that a branch pipe connecting to the liquid supply source is provided in the middle of the piping communicating with the liquid reservoir tank via a first change-over valve, and a constant flow amount valve making it possible to flow out a constant flow amount of liquid from the stern annular space to the outside of the vessel in accordance with a change-over operation of the first change-over valve is interposed in the branch pipe.
In the case that the structure is made in the manner mentioned above, the constant flow amount valve is operated due to changing over the flow passage by means of the first change-over valve so as to flow the constant flow amount of liquid from the front chamber to the rear chamber and further from the first seal ring to the outside of the vessel even when the hydrodynamic effect as screw type viscoseal caused by the fine screw groove formed on the sliding contact surface of the sleeve does not effectively function, whereby the cooling and lubricating state of the sliding contact surface can be maintained, and further it is possible to prevent the foreign substance and the seawater from entering.
Further, the first seal ring is generally arranged at the rearmost position (a position closest to the seawater), however, the structure may be made such that at least one auxiliary seal ring is further arranged on the seawater side of the first seal ring and the feeding means for forcibly feeding out the liquid to the outside of the vessel is provided on a sliding contact surface of the auxiliary seal ring and/or a sliding contact surface of an opposing element with which the auxiliary seal ring is slidably contacted.
Further, in the stern tube sealing apparatus in accordance with the present invention, piping connected to a ventilating line and/or a drain line communicated with an open air is provided in a second annular space adjacent to the interior side of the vessel of the stern annular space. Accordingly, in the case that a leakage is generated in the stern tube bearing lubricating oil, it is possible to recover the leaked lubricating oil within the vessel so as to prevent the lubricating oil from leaking to the outside of the vessel. Further, since a pressure of the liquid in the stern annular space is low and the second annular space is open to the air, it is possible to keep a differential pressure in the second seal ring in a small state.
Further, in accordance with the present invention, in the stern tube sealing apparatus mentioned above, the structure may be made such that a first branch pipe connecting to the liquid supply source is provided in the middle of the piping communicating with the liquid reservoir tank via a first change-over valve, a constant flow amount valve making it possible to flow out a constant flow amount of liquid from the stern annular space to the outside of the vessel in accordance with a change-over operation of the first change-over valve is interposed in the first branch pipe, a second branch pipe connecting to the air supply source is provided in the middle of the ventilating line via a second change-over valve, and an air relay to which the liquid pressure introduced by the constant flow amount valve is applied as a back pressure is interposed in the second branch pipe.
Further, in accordance with the present invention, in the stern tube sealing apparatus mentioned above, the structure may be made such that a branch pipe connecting to the liquid supply source is provided in the middle of the piping communicating with the liquid reservoir tank via a first change-over valve, a constant flow amount valve making it possible to flow out a constant flow amount of liquid from the stern annular space to the outside of the vessel in accordance with a change-over operation of the first change-over valve is interposed in the branch pipe, an oil feeding pipe connecting to the oil reservoir tank is provided in the middle of the ventilating line via a second change-over valve, and the oil reservoir tank is arranged so as to have an oil pressure lower than a feeding pressure of the constant flow amount fed to the stern annular space.
In the case that the structure is made in the manner mentioned above, it is possible to flow the constant flow amount of liquid from the first seal ring to the outside of the vessel by the constant flow amount valve even when the hydrodynamic effect as screw type viscoseal caused by the feeding means or the screw groove on the sliding contact surface of the sleeve does not effectively function, and it is possible to reduce a seal effect of the second seal ring and a contact abrasion between the second seal ring and the liner by the pressurized air or the oil fed to the second annular space.
Further, in the stern tube sealing apparatus in accordance with the present invention, the structure may be made such that an auxiliary seal ring is arranged on a further interior side of the vessel of a third seal ring arranged on an interior side of the vessel, and a branch pipe connected to an annular space defined by the third seal ring and the auxiliary seal ring from piping communicating with the stern tube chamber via a valve is provided. When the structure is made in the manner mentioned above, the auxiliary seal ring is in a standby state that a front surface pressure is the same as a back surface pressure and radial force of the seal ring itself and of a garter spring are only loaded when the valve is in an open state in the state that an oil pressure of the stern tube chamber is applied by a head pressure of the oil reservoir tank, so that it is possible to prevent an oil leakage of the stern tube chamber by closing the valve when the function of the third seal ring is damaged so as to function the auxiliary seal ring. Further, in the case that the pump is provided in the middle of a stern tube chamber circulating passage so as to circulate the oil, the auxiliary seal ring does not receive the radial force of the seal ring and the garter spring by flowing the oil from the annular space to the stern tube chamber through the auxiliary seal ring in accordance with adjustment of the valve, and it is possible to keep a further improved state as a standby state.
Further, in the stern tube sealing apparatus in accordance with the present invention, the liquid forcibly fed out to the outside of the vessel (the seawater side) may be set to a liquid which does not damage the water or seawater even when being mixed in the water or the seawater.